Hitherto, as food keeping means, a desiccating agent such a silica gel, quick lime, etc., and a deoxidating agent mainly composed of iron powder are known. Also, there are a method of enclosing the aforesaid desiccating agent or a deoxidating agent in a food-containing package to remove moisture or oxygen required for the growth of microorganisms in the package; a method of utilizing the sterilizing power of alcohol, i. e., a method directly adding or spraying a liquid alcohol addded, if necessary, with a perfume to foods or directly enclosing the alcohol in a package simultaneously with packaging a food, and an indirect alcohol addition method of enclosing an alcohol-enclosed bag or container in a food-containing package to give an antiseptic action and antimold activity by the alcohol vapor diffused from the bag.
In these methods, the indirect alcohol addition method can keep the effect successively after temporarily opening the food-containing package since the alcohol vapor is continuously diffused from the bag or container for a long period of time and such a method is proposed in, for example, Japanese Patent Publication No. 2273/'80. That is, according to the method described in Japanese Patent Publication No. 2273/'80, a so-called powder alcohol prepared by absorbing ethanol onto a solid absorptive material is enclosed in a bag or container made by a laminate of finely perforated polyethylene film or polyester film and a paper but this method has the following problems.
(1) When a food contains water, an oil, etc., the bag is swelled or the paper layer is wetted, which makes the bag unsuitable for a food keeping means.
(2) When a trade name, instructions for use, designs for improving beauty sight, etc., are printed on the surface of the bag or container the food quality keeping agent, the printing ink is dissolved out or left out because of oil in the food.
Also, as another indirect alcohol addition method, there is known a method of enclosing a liquid containing ethanol in a container at least one layer of which is composed of an ethylene-vinyl acetate copolymer film, etc., having excellent permeability for ethanol vapor, whereby the ethanol gas is diffused out through the film as described in Japanese Patent Laid-open No. 141,182/'80.
However, in the case of the foregoing method, heat sealing is required for sealing the container after packing a contents in the container, but since the film is melted by the heat at heat sealing and the molten film thus formed sticks to a sealing bar, high speed packing work is impossible by the method and the method is lacking in practicability.
For solving these problems, there is provided a method of laminating a heat-resisting paper to the non-sealing surface of the film, whereby the printability and shielding properties of the film are also improved but there are further problems about oil resistance and water resistance.
As a method of improving the oil resistance and water resistance of a paper, there is known a method of coating a liquid containing a water-dispersing fluorine compound as an oil resisting agent, a penetrating agent and a water repellent as necessary components on a paper or impregnating a paper with the foregoing liquid. However, the oil resisting sheet obtained by the method is insufficient in an alcohol resistance. That is, there is a problem that the oil resistance of the sheet is reduced with the passage of time in the presence of alcohol.